1. Field of the Invention
The present invention relates to a method for producing a color filter, using a dry etching process.
2. Description of the Related Art
As methods for manufacturing a color filter for use with a liquid crystal display device or a solid image pickup element, dyeing methods, printing methods, electrodeposition methods, and pigment dispersion methods are known.
In the pigment dispersion method, the color filter is produced by a photolithographic method using a colorant-containing radiation-sensitive composition prepared by dispersing a pigment in any one of various types of photosensitive compositions. The color filter produced by this method is stable with respect to light, heat and the like since the pigment is used. A high positional accuracy can be obtained in this method since patterning is performed by the photolithographic method, and accordingly, this method has widely been used as a method suitable for producing a color filter for a color display with a large screen and high fineness.
In a case in which the color filter is produced by the pigment dispersion method, the radiation-sensitive composition is first coated onto a glass substrate by using, for example, a spin coater or a roll coater and then dried, to thereby form a coating film. Then, colored pixels are obtained by pattern-exposing and developing the thus-formed coating film. The color filter can be obtained by repeating such an operation as described above for each of the different colors.
As for the pigment dispersion method, a method which uses a negative photosensitive composition comprising an alkali-soluble resin together with a photopolymerizable monomer and a photopolymerization initiator is proposed in each of, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 2-181704, 2-199403, 5-273411 and 7-140654.
In recent years, it has been desired that color filters for solid image pickup elements be made minuter and finer, and techniques using a dye have been suggested (see, for example, JP-A No. 6-75375). However, curable compositions which contain a dye have a problem in that various performances such as light resistance, heat resistance, solubility, and uniform coating property are in general poorer than in compositions which contain a pigment. Moreover, when such a curable composition is used, in particular, for the production of a color filter for a solid image pickup element, the curable composition is required to provide a film thickness of 1.5 μm or less; therefore, it is necessary to add a large amount of a colorant into the curable composition. This causes a problem in that the pattern-formability of the composition is remarkably low for the following reasons: the adhesion between the film and the substrate becomes insufficient; a sufficient curability cannot be obtained; the dye is missing in the light exposure region; and other defects are caused.
In liquid crystal display devices and solid image pickup elements, reduction in the pixel size thereof has been advancing. Thus, it has become necessary to decrease the size of color filters as well. Reduction in the size of solid image pickup elements has been particularly remarkable, and thus, it has been necessary to use a technique providing a high resolution below 2.0 μm. Thus, in conventional photolithographic methods, the resolution thereof has been approaching a limit.
Apart from the above-mentioned color filter producing method using photolithography, a dry etching process has been hitherto known as a process effective for forming a thinner and finer pattern. The dry etching process has been hitherto adopted as a process for forming a pattern with respect to a thin film made of an evaporated colorant (see, for example, JP-A No. 55-146406). This process makes it possible to form a thin film which can have a thickness as small as ½ or less of the thickness obtained by photolithography and have spectral characteristics as good as those obtained by photolithography. Furthermore, a pattern forming process wherein photolithography is combined with a dry etching process has also been proposed (see, for example, JP-A No. 2001-249218).
However, in the formation of a thin film by evaporation (vapor deposition), an evaporating device is unavoidably polluted. Thus, a large burden is imposed on the production of color filters. Moreover, their pixels are made only of a pigment or dye. For this reason, the adhesion of the pixels to an underlying flattening layer or an upper layer is bad, and this is one of the reasons that the yield does not rise.
Moreover, the color filter producing method based on dry etching has a problem in that when a second colorant-containing layer is formed and etched, it is difficult to simultaneously remove the coloring material of the second layer applied on the first layer and the coloring material of the second layer coated in a region where the first layer has been removed. In the case of separately removing the coloring material of the second layer applied on the first layer and the coloring material of the second layer coated in the region where the first layer has been removed, there arise problems in that the number of steps increases and costs increase.